Method and apparatus for treating air



Feb. 17, 1942. F. HIBBERD MEN- OD AND APPARATUS FOR TREATINGAIR .Fi ledMay 24, 1938 6W WW? Patented Feb. 17, 1942 METHOD AND APPARATUS FOR.TREATING Frederick Hyde Hibberd, Harrison, N. Y. Application May 241938, Serial N0. 209,652

13 Claims.

This invention relates to air conditioning and more particularlyconcerns a method and apparatus.for cooling and dehumidifying the air inrooms or other enclosures used for human occupancy.

The conditioning of air in the warmer seasons and climates involvescooling and dehumidiflcation, and is usually accomplished by reducingthe air temperature to a value below its dew point whereby water iscondensed therefrom, after under treatment. Due to the relatively highcost of controls for independently varying the re- 'which the air isre-heated, by mixture with unto the low temperatures necessary tocondense moisture therefrom. The large size and relatively highinstallation a d operating costs of the refrigerating mechan m, which isusually of the compression type, has been a deterrent to theinstallation of air.conditioning equipment,

particularly in homes, offices and other relatively small enclosures. Inthe past, the more economically operating air conditioning systems haveemployed a single relatively large air conditioning unit, from whichconditioned air is distributed through ducts to the various rooms orspaces to be conditioned. The installation of such systems in existingbuildings is diflicult and expensive and such installations are notordinarily feasible where a relatively small proportion of the rooms,apartments or oflices in a building are ,to be conditioned.

It has heretofore been proposed to provide relatively small cooling or'air conditioningunits for installation in ofiices, apartments or rooms.Be-

frigerating and dehumidifying effect in such systems, room units of thetype described are customarily furnished without controls and are merelyturned on or off as needed. This gives inaccurate results since therelation between the humidity load and the temperature load varieswidely under different conditions of room occupancy and outdooratmosphere.-

With the above and other considerations in mind, it is proposed inaccordance with the present invention to provide an improved andeffective air conditioning method and apparatus which, by reason ofitsunique operating characteristics, may be installed and operated at alow cost, and in which the dehumidifying and cooling efiects producedmay be independently regulated. A further object of the inventioncomprises the provision of an air conditioning method and apparatuswhich is readily adapted to installation in the form of small permanentor portable roomtype units which do not require water supply or drainconnections, window outlets or air ducts.

.Further objectsof the invention include the pro- In general, the aboveand other objects of the j .-invention' are carried out by employingaprimary solution which may be water or a hygroscopic solution of asuitable salt such as lithium chloride or calcium chloride,simultaneously cooling and dehumidifying the air to be conditioned by.contact with this solution, transferring heat and moisture from theprimary solution to a seconcause of certain inherent disadvantages, suchunits have not been widely adopted. These units cool and dehumidify theair by passing it over a refrigerating coil and employ compression typerefrigerating mechanism which must be cooled by circulating air or waterthereto to absorb heat dar'y solution which is preferably a hygroscopicsalt solution, and removing heat and moisture from the secondarysolution. The. secondary sofrom the compressed refrigerant. Watercooling requires the installation of water piping and drains, andprecludes both the portability of the unit and its use in rooms where asupply of water is not available. If air is used as the coolin medium,the unit musteither be located adjacent a window or connected with theoutside of the building through ducts of relatively large section.mechanism is noisy, is prone to develop refrigerant leaks and requiresthe provision of 'drains for Further, compression type refrigerating thedisposal of the water condensed from the air lution may be formed from ahygroscopic salt such as lithium chloride or calcium chloride. I preferto effect the transfer of heat and moisture from the primary to thesecondary solution by circulating air successively in contact with thetwo solutionsand' maintaining this air under partial vacuum whereby thetransfer of heat fromjthe secondary solution to the primary solution isminimized. In accordance with certain features ofiny-invention, the flowof the primary solution isutilized tomaintain th heat'and moisturetransferring "fluid under partial vacuum, and the flow of the secondarysolution is used to circulate the rarifled air or other medium whichtransfers heat and moisture from the primaryto the secondary solutiom'Additional features of the invention will beapparent from the followingdescription.

In describing the invention in detail, reference I will be made to theaccompanying drawing'in which the single figure represents, in adiagrammatic and simplified manner, an air conditioning system embodyingmy invention.

In general, my improved air conditioning sysv tern comprises three fluidcircuits, namely, a primary solution circuit in which the primarysolution is successively passed in contact with the air to be treatedand with dry rarified air which removes heat and moisture from theprimary solution, a transfer circuit in which air at subatmosphericpressure is circulated successively in contact with the primary solutionand the ing to the room through the upper outlet port 4. The fan may bedriven by suitable means such as an electric motor, not shown. One ormore eliminator mats or filters 5 are preferably disposed across theinterior of the casing I between the air inlet and outlet ports 3 and 4.These mats may be formed of any suitable material such as shreddedfibrous matter held between screens. The primary solution is sprayeddownwardly in the casing I from a spray pipe 6 or equivalent means whichis preferably situated between the two eliminator mats 5. After theprimary solution has passed in contact with the.

downwardly from suitable means III in a flue II within the chamber 9.The flue II is preferably provided with eliminator mats or filters I2which may be similar to the mats 5-ln the air treatment casing I. Thetransfer chamber 9 is so constructed as to form aclosed circuit for thecirculation of rarified air or other heat and moisture transferringmedium, the course of this circuit being indicated by the arrows. Asshown, the upper end of the flue I I is connected through a downwardlyextendingpassage I3 and a horizontal passage I4 to the lower end of avertical absorption flue I5, through which the secondary hygroscopicsolution is passed as hereinafter described. The upper end of the flueI5 is connected through a-fan casing I6 and a downwardly extendingpassage I1 to the lower endof the evaporation flue II.

flue I5, and a fan I9 in the casing I6 circulates the transfer fluidthrough the circuitjust traced.

In accordance with my invention, the fluid circulated in the transferchamber 9 is preferably under a partial vacuum which is preferof mercuryis so rarified that it cannot carry sub-.

room air flowing through the casing I, it falls into a sump I from whichit is removed by a pipe 8 under the control of a float valve orequivalent means 9'.

The primary solution may be pure water, and satisfactory results areobtained when water is used for this purpose. I have found however, thata. considerably wider range of control of room air temperature andhumidity is obtainable when a solution of a hygroscopic salt such aslithium chloride or calcium chloride is used as the primary solution. Inthis specification and the appended claims the term primary solutionwill be used broadly to designate both water and a hygroscopic saltsolution of the type indicated.

As the relatively cool primary solution passes in intimate contact withthe air under treatment in the casing I,'it both cools and condenses orabsorbs moisture from this air, thus simultaneously lowering therelative humidity and the dry bulb temperature of the air expelledthrough the port 4 to the required values. The amount of cooling thuseffected is determined by the temperature of the incoming primarysolution, and when water is employed as the primary solution, itstemperature also determines the dehumidifying eflect. When a hygroscopicsalt solution is used, the dehumidifying effect is separately variablein accordance with the concentration of the primary solution coming intocontact with the air. The primary solution which passes off from the airtreatment casing I through the pipe 8 isrelatively warmer and con--'tains the moisture it has absorbed or condensed from the treated air. 4

The primary solution next enters a transfer chamber 9 through the pipe 8and is sprayed ably 15 inches of mercury or higher,'and may be in theneighborhood of 25 to 28 inches of mercury. The fluid in this chambermay comprise air or other inert gas. The purpose of maintaining thechamber 9 under partial vacuum is to avoid substantial transfer of heatfrom the secondary hygroscopic solution passing through theflue I5 tothe primary solution in the flue II. Air under a vacuum of about 25 to28 inches this air from the primary solution falling through the flueII. This evaporation of moisture in the previously dehumidifled airconcentrates the primary solution if a salt solution is used and in anycase, cools this solution due to the absorption of heat as latent heatof vaporization. The amount of moisture evaporated from the primarysolution to the air in the flue II is somewhat greater than. the amountof moisture previously condensed or asorbed by the primary solution fromthe room air in the air treatment casing I. This is so because inregenerating the primary solution, it is not only necessary to removethe moisture it has condensed or absorbed, but also to remove the heatdelivered to this solution as sensible heat from the room air in thecasing I. Accordingly, the amount of moisture evaporated from theprimary solution in the flue II cortesponds to the sum of thedehumidifying and cooling effects produced on the room air beingconditioned. The excess of moisture removed from the primary solution inthe flue II over that scribed.

The cooled primary solution falls to the bottom of the flue II and isdrawn out of the transfer chamber 9 through the pipe 20 by a circulatingpump 2|, driven by suitable means such as an electric motor 22. The pump2| returns the cooled primary solution through pipes 23 and 24 to thespray pipe 6 of the air treatment casing I.

The transfer chamber 9 may be maintained under partial vacuum by anysuitable known Transverse eliminatorf mats or filters I8 are preferablyprovided in the means. In accordance with one feature of the invention,I prefer to employ the circulating primary solution for this purpose. Asshown, a jet ejector or evacuator E of known construction is suppliedwith motive fluid comprising the return primary solution from the pipe23, and the suction inlet of the ejector is connected to the trans"-'fer chamber 9 through a pipe 25. The ejector discharges into the airtreatment casing supply pipe 24. Although higher degrees of vacuum maybe used with satisfactory results, I prefer to reduce the operating costof the system by maintaining a vacuum in the chamber 9 which is belowthat necessary to produce ebullition or flashing off of the primarysolution in this chamber. Since the purpose'of maintaining the chamber 9under partial vacuum is to rarify the air therein to a point where heattransfer by the return air is maintained at a negligible value,comparatively low vacuums (15 to 28 inches of mercury) with attendantpower economies-can be used. The ejector E may be suitably adjusted tomaintain the desired vacuum by any suitable means, such as the valve 26in the suction pipe 25.

The secondary hygroscopic solution, in a highly concentrated condition,enters the transfer chamber 9.at the top of the flue l through.

a nozzle 21 and flows downwardly in spray form through this flue incontact with" the rising stream of rarifled air and water vapordelivered from the absorption flue I! through the passages l3 and I4.Water vapor is absorbed from the rarified air by the secondary solutionin the flue i5, and the solution is consequently heated and diluted. Thedry and dehumidifled air is increased and then enters the evaporatingpan 38 of a first effect evaporator A. The solution in the pan 38 isheated by suitable means, such as the electric heating coil'39, and thewater vaporor steam evolved passes out of the evaporator A through apipe 40 and to the heating coil 4| in the pan 42 of the secondary effectevaporator B. The secondary solution which has been concentrated in thefirst efiect evaporator A flows over one end of the pan 38 and out ofthe evapodenser coil 48 located in the sump 29 of the absorption fluel5, and is there condensed, delivering heat to the dilute secondarysolution in this sump. From the condenser 48, the water flows to theprimary circuit pipe'2ll through the pipe 49. The water thus returned tothe primary solution circuit at least partially compensates for theexcess of water evaporated from the circuit in the transfer chamber 9over the water absorbed or condensed by that solution from the air undertreatment. Further, the connection bedelivered from the top of the flue15 through the passage I! to the bottom of the evaporation flue ll.

The rarified air in the chamber 9 may be circulated by any suitablemeans, andin accordance with one feature ofmy invention, the kineticenergy of the incoming secondary solution is employed for this purpose.As shown, the air circulating fan I9is connected to and driven by animpulse turbine 28 or equivalent means disposed in the path of the jetof secondary solution entering the fine l5 from the nozzle 21. Thisarrangement not only eIfects operating economies but permits thelocation of all moving parts of the air circulating means within thepartially evacuated transfer chamber 9, and the provision of stuffingboxes with attendant hazard of leaks is avoided.

The secondary solution which has absorbed,

heat and water from the transfer fluid collects in a sump 29 and isdrawn off through a pipe 30 by a pump 3| which may conveniently bedriven by the motor 22 as shown. This diluted secondary solution is at arelatively high temperature and is passed through a circuit in which itis concentrated by the evaporation of moisture therefrom and cooled byheat exchange with a suitable medium such as the outdoor air.

The secondary solution may be concentrated by various means, and in thedisclosed embodiment, a two effect evaporator is employed for thispurpose. The dilute secondary solution is delivered by the pump 3|through a pipe 32, and a portion of this solution is diverted through apipe 33 to the evaporator system. The amount of secondary solution sodiverted may be controlled by suitable-means, such as the valves 34 and35. In the evaporator system, the secondary solution passes successivelythrough the heat exchangers 36 and 31 where its temperature is tween thesecond effect evaporator B and the outlet pipe 20 of the transferchamber 9 maintains the evaporator B under partial vacuum and therebypromotes evaporation of water from the secondary solution in thisevaporator at the relatively low temperature produced by the exhauststeam from the first efiect evaporator A. If desirable or necessary, thepipe 49 may be restricted by a suitable orifice or a valve 50 so thatthe condenser 48 may be maintained at a high enough pressure to insurethe condensation of water vapor or steam therein.

The current supplied to the heating coil 39 is preferably regulated inaccordanc with the temperature of the solution in ,the evaporator A sothat a substantially constant degree of concontrol mechanism 68controlled by the element 61. In order to prevent the withdrawal of allthe liquid from the evaporator A and a consequent breaking of the vacuumin the evaporator B, a valve 69 is provided in the pipe 44, and thisvalve is preferably controlled in accordance with the liquid level inthe evaporator- A by suitable means such as the float mechanismillustrated at 10.

The relatively hot concentrated secondary solution may be cooled by heatexchange with any suitable medium. In installations where tap water orother cooling medium supply is readily available and not too expensive,this solution may-be cooled by heat exchange with such water ormedium.It is usually preferable and 'often necessary to operate.- the systemwithout any supply of'water, and my system is admirably adapted to suchinstallations in that the secondary solution may be cooled by directheat exchange with theoutdoor air. As shown in the drawing, thehot-concentrated secondary solution passes through a pipe 5|, a'heatexchanger 52 and a pipe 53to a cooling coil 54 which is preferablylocated in the outdoor atmosphere outside the wall 55 of the building inwhich air is to be conditioned. The coil 54 may be cooled by convectioncurrents, but it is generally preferred to provide a motor driven fan 55to circulate air over this coil. The cooling effect may be increased bycooling the outdoor air delivered to the coil 54, or at least theportion of such air which comes into contact'with the final portions ofthis coil from which the cooled secondary solution is discharged. Thismay be adcomplished by spraying water from a spray pipe 51 into the airdelivered by the fan 55 to the outlet end of the coil 54, and water forthis purpose may comprise the condensate from the heating coil 4| of thesecondary eifect evaporator B, delivered through pipes 58 and 59 andheat exchanger 52. The heat exchanger 52 is not essential, but may beused to cool the condensate by heat exchange with the secondarysolution. The cooled and concentrated secondary solution is returnedfrom the cooling coil 54 through the pipe 50 to the nozzle 21 in theabsorption flue I5 of the transfer chamber 9, thus completing thecircuit. The amount of water returned to the primary solution from theevaporator B may be supplemented by supplying a controlled amount ofcondensate from the heating coil H to the air treatment casing I throughthe pipe 5|. The amount of water so returned may be regulated by thevalve 52, and the amount of water supplied to the spray pipe 5'! may becontrolled by a valve 53.

In operating the system with hygroscopic salt solutions in both theprimary and secondary solution circuits, the temperature andconcentration of the hygroscopic salt solutions is so regulated as toproduce the desired air cooling and dehumidifying effects. In a typicalcase, with the primary solution entering the air treatment casing I atabout 65 F. and about 55 F, water vapor pressure (that is, a vaporpressure corresponding to that of water at 55 F.) and leaving thiscasing at about 75 F. and 65 F. water vapor pressure, the secondarysolution may enter the transfer chamber 9 through the nozzle 21 at about95 F. and 43 F, water vapor'pressure, and leave this chamber at about110 F. and about 58 F. water vapor pressure. A relatively smallproportion of the secondary solution, of the order of is by-passedthrough the evaporator system, and this solution may be heated, in theexchangers 35 and 31, from about 110 F. to about 260 F, Theconcentrated.

solution may leave the first effect evaporator A at about 280 F. andenter the second effect evaporator B, after giving up heat in theexchanger 31 at about 210 F. The concentrated solution from the secondeffect evaporator B may have a concentration of about 45% and may be atabout 120 F. after leaving the exchanger 35. The condensate fromthesecond effect evaporator B may be cooled from an initial temperature ofabout 200 F. to about 125 F. in passing through the heat exchanger 52.If water is used as the primary solution, it may enter the air treatmentcasing at a somewhat lower temperature, in the neighborhood of 55 F.

The cooling and dehumidifying efiects may be variably controlled bysimple valveadjustments. Thus by adjusting a valve -I54, which regulatesthe proportion of returned primary'solution delivered to the spray pipe5 and the .proportion by-passed through the pipe II, the amount ofprimary solution passed into contact with the room air may ,be altered,whereby the cooling effect may be changed. This-operation maybe'performed in response to changes in room air temperature by employinga suitable temperature responsive device or thermostat T connected tooperate a bypass valve 55 in the primary solution supply pipe 24. Thedehumidifying efiect may be variably controlled by varying the amount ofmoisture returned from the secondary solution to the primary solution inthe air treatment casing I by suitable adjustment of the valve 52. If ahygroscopic salt solution is employed as the primary solution, thereturn of water thereto lowers its concentration and accordinglydecreases the amount of moisture it absorbs from the room air. Thereturn of moisture to the primary solution in the casing I may be variedin accordance with changes in the relative humidity of the room air byemploying a hygrostat or wet bulb thermostat H connected to operate asuitable valve 55 in the pipe 5I through which moisture from thesecondary solution is returned. The temperature and humidity responsivedevices T and H as well as the valve mechanisms 55 and 55 operatedthereby may be of any suitable known construction.

The extent to which the secondary solution is concentrated may bevariably controlled by regulating the proportion of this solution whichis diverted through the evaporator system by adjustment of the valves 34and'35. The amount of concentration may be further adjusted by suitablyregulating the control thermostat 51 governing the energy delivered tothe heating coil 39 in the first effect evaporator A.

As will be evident from the foregoing description, my improved methodconsists generally in.

absorbing heat and moisture from the room air by contact with a primarysolution, transferring the heat and moisture so absorbed from theprimary solution to a secondary hygroscopic salt solution, preferably bycirculating a rarified inert gas in successive contact with the twosolutions, and concentrating and cooling the secondary solution. By thismethod, the heat, absorbed from the room air may be dissipated to theoutdoor air at relatively high temperatures and without the use ofcompression apparatus. Since air cooling is used and the moistureabsorbed from the room air is disposed of by evaporating it to augmentthe cooling efiect of the outdoor air on the heat dissipating coil 54,

the method can be performed without the use of either cooling water ordrain connections. Further, since the heat resulting from airconditioning and also theheat of evaporation evolved in concentratingthe secondary solution is dissipated from a single solution only, andthe useof compression or other refrigerating apparatus requiring coolingis avoided, the method can be carried out without the use of bulky airducts, and all window connections except a very small duct or openingfor fresh air supply are eliminated. The system maybe constructed in theform of a compact portable unit having small flexible tubularconnections (comprising the pipes 53, 59 and 5D) to an outdoor coolingcoil, and with this arrangement, the air conditioning unit can be placedat any convenient point in a room or apartment without regard toexisting window, water pipe or drain arrangements. The electric currentconsuming devices of the system, comprising the motors for driving thefans 2 and 56, the pump motor 22 and the heating unit 39, are all ofrelatively small capacity and accordingly may'be individually connectedto ordinary house lighting circuits without danger of overloads.

I claim:

1. A method of conditioning air in an enclosure which comprisescirculating a primary solution in successive contact with the air in theenclosure and rarefied and dehumidified air whereby heat and moistureare removed from said enclosure air by said primary solution andtransferred from said primary solution to said rarefied air byevaporation, circulating said rarefied air successively in contact withsaid primary solution l and a secondary hygroscopic solution wherebymoisture evaporated from said primary solution in said rarefied air isabsorbed by said secondary solution, evaporating the moisture soabsorbed from said secondary solution by the application of heatthereto, cooling the secondary solution by heat exchange with a coolingmedium and returning the cooled and concentrated secondary solution intocontact with said rarefied air.

2. A method of conditioning air in an enclosure which comprisescirculating a primary solution in successive contact with the air in theenclosure and rarefied and dehumidified air whereby heat and moistureare removed from said enclosure air by said primary solution andtransferred from said primary solution to said rarefied air byevaporation, circulating said rarefied air successively in contact withsaid primary solution and a secondary hygroscopic solution wherebymoisture evaporated from said primary solution in said rarefied air isabsorbed by ture are absorbed from said primary solution by evaporationof moisture in said inert gas, maintaining said inert gas under partialvacuum by the circulatory movement of said primary solution, circulatingsaid inert gas successively in conbody of rarefied air whereby moistureremoved from the air under treatment by the primary solution isevaporated in said rarefied air, means.

for maintaining said rarefied air in its rarefied condition, means forcirculating said rarefied air in successive contact with said primarysolution and a secondary hygroscopic solution whereby moistureevaporated from said primary solution in said rarefied air is absorbedby and transferred to said secondary solution, means for evapsaidsecondary solution, evaporating the moisture so absorbed from saidsecondary solution by the application of heat thereto, cooling thesecondary solution by heat exchange with a cooling medium, returning apart of the moisture evaporated from said secondary solution to saidprimary solution and returning the cooled and concentrated secondarysolution into contact with said rarefied air.

3. A method which comprises circulating asolution and during itscirculation bringing it into' contact with a dehumidified inert gasunder partial vacuum, whereby heat and moisture are absorbed from thesolution by evaporation of moisture in the inert gas, maintainingsaidinert gas uncler partial vacuum by the circulatory movement of saidsolution, absorbing moisture from said inert gas and returning saiddehumidified inert gas into contact with said solution.

4. A method which comprises circulating a primary solution and duringits circulation bringing it into contact with a dehumidified inert gasunder partial vacuum whereby heat and moisture are absorbed from saidprimary solution by evaporation of moisture in said inert gas,circulating said inert gas successively in contact with said primarysolution and a concentrated secondary hygroscopic solution wherebymoisture evaporated from said primary solution in said gas is absorbedfrom said gas by said secondary solution, circulating said secondarysolution successively in contact with said inert gas and throughevaporating and cooling means, and employing the circulatory movement ofsaid secondary solution to circulate said inert gas.

5. A method which comprises circulating aprimary solution and during itscirculation bringing means for circulating a primary solution, a closedsaid chamber. I

orating moisture from said secondary solution, means for cooling saidsecondary solution, and means i'orreturning the cooled and concentratedsecondary solution into contact with the rarefied air.

.7. Apparatus of the kind described comprising means for circulating aprimary solution,

a closed chamber through which said primary solution passes during itscirculation, means operated by such circulation of said primary solutionfor maintaining said chamber under a partial vacuum, means forcirculating a secondary hygroscopic solution successively through saidchamber and through moisture evaporating and cooling apparatus, andmeans for circulating rarefied air in successive contact with saidprimary solution and said secondary solution in 8. Apparatus of the kinddescribed comprising chamber through which said primary solution passesduring its circulation, means for maintaining said chamber under apartial vacuum, means for circulating a secondary hygroscopic solutionsuccessively through said chamber and through moisture evaporating andcooling apparatus, and

means operated by the circulation of said secondary solution forcirculating rarefied air in successive contact with said primarysolution and said secondary solution in said chamber.

9. Apparatus of the kind described comprising means for circulating aprimary solution, a closed ,chamber' through which said primary solutionpasses during its circulation. means operated by such circulation ofsaid primary solution for maintaining said chamber under a partialvacuum, means for circulating a secondary hygroscopic solutionsuccessively through said chamher and through moisture evaporating andcoolunder partial vacuum whereby heat and mois ing apparatus and meansoperated'by'the circulation of said secondary solution for circulatingrarefied air in successive contact with said primary solution and saidsecondary solution in said chamber.

10. Apparatus of the kind described comprising, means for circulating aprimary solution, means for transferring moisture from said primarysolution to a secondary hygroscopic solution, means for evaporatingmoisture from said secondary solution whereby said secondary solution isconcentrated, means for condensing the a moisture so evaporated fromsaid secondary solution, means for returning a part of the moisture socondensed to said primary solution, a cooling coil, means for passingsaid concentrated secondary solution through said cooling coil from endto end thereof, means for passing, a stream of outdoor air in contactwith said cooling coil and means for evaporating a part of saidcondensed moisture in the part of said outdoor air stream which contactsthe portion of said coil-adjacent the end thereof from which saidsecondary solution is discharged. 1

11. Apparatus of the kind described comprising a closed chamber, meansfor passing a solutionthrough said chamber, means for circulating air insaid chamber in successive contact closed chamber through'which theprimary solution passes during its circulation, means for circulating asecondary hygroscopic solution through said closed chamber, meanstorcirculating an inert gas in said closed chamber in successive contactwith said primary solution and said secondary solution, evaporator meansfor evaporating moisture from said secondary solution, means operated bythe circulation of said primary solution for maintaining said closedchamber under partial vacuum and means for condensing some of the vaporfrom said evaporator means by heat exchange with the secondary solutionas it leaves said closed chamber.

13. Apparatus of the kind described comprising means for circulating aprimary solution, a closed chamber through which the primary solutionpasses during its circulation, means for circulating a secondary.hygroscopic solution through said closed chamber, means for circulatingan inert gas in said closed chamber in successive contact with saidprimary solution and said secondary solution, evaporator means forevaporating moisture from said secondary solution, means for maintainingsaid closed chamber under partial vacuum, means for maintaining saidevaporator means under partial vacuum, and means for condensing vaporfrom said evaporator means by heat exchange with said secondary solutionas it leaves said closed chamber.

FREDERICK HYDE HIBBERD.

